The invention relates to microelectro-mechanical actuator devices and the use of arrays of these devices to provide reconfigurable circuits.
A common method of tuning prototype microwave circuits, or even fine tuning production circuits, is to selectively add or subtract tuning elements from the circuit while monitoring the effect of such tuning on a network analyzer. In the case of a microstrip circuit, the addition or subtraction of conductor metal, which changes the size and shape of the microstrip line, will alter the impedance characteristics of that line.
The advantage of this technique is that compensation can be added to account for differences in xe2x80x9cidealxe2x80x9d modeled matching networks and the xe2x80x9creal worldxe2x80x9d realization of those networks. In fact, it is not necessary for a modeled matching network to exist. A component can be matched to the preceding and following stages working from xe2x80x9cscratchxe2x80x9d with no prior knowledge of the circuit matching requirements. These techniques add flexibility to circuit design by allowing microwave integrated circuits (MICS) to be modified quickly without the need of a complete fabrication cycle run.
Disadvantages of this technique are that it takes a skilled and patient operator to tune the circuit and secure the tuning elements so that the performance of the circuit remains constant over time. Positioning of tuning elements is quite tedious as errors in element positioning of a few thousandths of an inch will dramatically affect circuit performance, especially at higher frequencies. These problems also make repeatability a problem. It is very difficult to manually reproduce a certain arrangement of tuning elements.
Conventional microstrip circuits are fine tuned by hand to optimize performance with modeled impedance matching networks that are fabricated on the substrate along with xe2x80x9cchicken dotsxe2x80x9d or xe2x80x9cconfettixe2x80x9d to which additional tuning elements can be attached, if necessary. In this case, gold mesh patterns are added to the circuit and attached with a thermo-compression bonder.
A means by which tuning elements can be modified quickly, easily, and repeatably would significantly impact microwave circuit design and implementation. Tuning elements which can be reconfigured remotely and on demand would open up a new area of dynamic circuit tuning.
The invention is the mechanism which provides the aforementioned tuning capabilities. One application of the invention is to fabricate an array of microelectro-mechanical system (MEMS) tuning elements described herein as part of a microwave circuit. Deploying selected portions of the array would be the equivalent of adding metal conductor pattern to the microwave circuit. The MEMS tuning elements can be deployed in whatever pattern necessary to realize the appropriate microwave circuitry. The deployment of the individual tuning elements can be computer controlled, giving this technique great advantages over the manually tuned method described above. It is also possible to reconfigure the MEMS tuning element array to realize any circuit configuration desired. These modifications of the microwave circuit can be realized very quickly with great accuracy and repeatability.
The application of the MEMS tuning elements described above is but one of many uses envisioned. Some other applications are described hereinafter with reference to exemplary embodiments.
Accordingly, the invention provides a microelectro-mechanical device which includes a fixed electrode formed on a substrate, the fixed electrode including a transparent, high resistance layer, and a moveable electrode formed with an anisotropic stress in a predetermined direction and disposed adjacent to the fixed electrode.
The device includes first and second electrically conductive regions which are isolated from one another by insulator layers on the moveable and fixed electrodes and/or by an air gap, the moveable electrode being electrically coupled to the first conductive region. The moveable electrode moves close to and covers the fixed electrode, which changes the electrical coupling to the second conductive region, thus enhancing the electrical coupling of the first and second conductive regions, in response to a potential being applied across the fixed and moveable electrodes. The enhanced electrical coupling between the moveable electrode and the second conductive region is small when the moveable and fixed electrodes are far apart, and thus there is a high resistance or high impedance. When the two electrodes are close together, there is a high coupling, low resistance or low impedance contact. The fixed electrode is transparent to electromagnetic signals or waves and the moveable electrode impedes or allows transmission of electromagnetic signals or waves through the device depending on its position relative to the first and second conductive regions. In one embodiment of the invention, the fixed and moveable electrodes are configured within an array of similar devices, and each device or groups of devices in the array are individually addressable to actuate the moveable electrodes.
In another embodiment of the invention, there is provided a reconfigurable circuit including an array of actuatable devices which are addressed individually or in selected groups, each of the actuatable devices having a fixed electrode formed on a substrate, the fixed electrode including a transparent, high resistance layer, and a moveable electrode formed with an anisotropic stress in a predetermined direction and disposed adjacent the fixed electrode. Each of the actuatable devices includes first and second electrically conductive regions which are isolated from one another by the fixed electrode, the moveable electrode being electrically coupled to the first conductive region. The moveable electrode moves to cover the fixed electrode and to electrically couple to the second conductive region, thus electrically coupling the first and second conductive regions, in response to a potential being applied across the fixed and moveable electrodes. The fixed electrode is transparent to electromagnetic signals or waves, and the moveable electrode impedes or allows transmission of the electromagnetic signals or waves depending on its position relative to the first and second conductive regions.